Fin field effect transistor device structure and method for forming the same

ABSTRACT

A method for forming a fin field effect transistor device structure includes forming a fin structure over a substrate. The method also includes forming an isolation structure surrounding the fin structure. The method also includes cleaning sidewalls of the fin structure. The method also includes depositing a silicon cap layer over the fin structure. The method also includes growing an oxide layer over the silicon cap layer. The silicon cap layer is thinned after growing an oxide layer over the silicon cap layer. The method also includes forming a gate structure over the oxide layer across the fin structure. The method also includes growing a source/drain epitaxial structure beside the gate structure. The method also includes forming a contact structure electrically connected to the gate structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/967,731, filed on Jan. 30, 2020, the entirety of which isincorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon. Many integratedcircuits are typically manufactured on a single semiconductor wafer, andindividual dies on the wafer are singulated by sawing between theintegrated circuits along a scribe line. The individual dies aretypically packaged separately, in multi-chip modules, for example, or inother types of packaging.

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as thefin field effect transistor (FinFET). FinFETs are fabricated with a thinvertical “fin” (or fin structure) extending from a substrate. Thechannel of the FinFET is formed in this vertical fin. A gate is providedover the fin. The advantages of a FinFET may include reducing the shortchannel effect and providing a higher current flow.

Although existing FinFET devices and methods of fabricating FinFETdevices have generally been adequate for their intended purposes, theyhave not been entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a perspective representation of a FinFET device structure, inaccordance with some embodiments of the disclosure.

FIGS. 2A-2E, 2F-2, 2G-2 are cross-sectional representations of variousstages of forming a FinFET device structure, in accordance with someembodiments of the disclosure.

FIGS. 2F-1 and 2G-1 are perspective representations of a FinFET devicestructure, in accordance with some embodiments of the disclosure.

FIGS. 3A-3G are cross-sectional representations of various stages offorming a modified FinFET device structure, in accordance with someembodiments of the disclosure.

FIGS. 4A-4C are cross-sectional representations of various stages offorming a modified FinFET device structure, in accordance with someembodiments of the disclosure.

FIGS. 5A-5F are cross-sectional representations of various stages offorming a modified FinFET device structure, in accordance with someembodiments of the disclosure.

FIGS. 6A-6C are cross-sectional representations of various stages offorming a modified FinFET device structure, in accordance with someembodiments of the disclosure.

FIG. 7 is a cross-sectional representation of a FinFET device structure,in accordance with some embodiments of the disclosure.

FIGS. 8A-8B are cross-sectional representations of various stages offorming a modified FinFET device structure, in accordance with someembodiments of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. It should be understood that additionaloperations can be provided before, during, and after the method, andsome of the operations described can be replaced or eliminated for otherembodiments of the method.

Fin structures described below may be patterned by any suitable method.For example, the fins may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers may then be used to pattern the fins.

Herein, the terms “around,” “about,” “substantial” usually mean within20% of a given value or range, and better within 10%, 5%, or 3%, or 2%,or 1%, or 0.5%. It should be noted that the quantity herein is asubstantial quantity, which means that the meaning of “around,” “about,”“substantial” are still implied even without specific mention of theterms “around,” “about,” “substantial.”

Embodiments for forming a fin field effect transistor (FinFET) devicestructure are provided. The method for forming the FinFET devicestructure may include forming a cap layer over the fin structure. Aftergrowing a gate dielectric layer over the cap layer, the cap layer may beconsumed but remain over the fin structure. With the protection of thecap layer, the width of the fin structure may remain after growing theoxide layer. Therefore, the width of the fin structure may be preciselycontrolled.

FIG. 1 is a perspective representation of a FinFET device structure 10a, in accordance with some embodiments of the disclosure. FIGS. 2A-2E,2F-2, 2G-2 are cross-sectional representations of various stages offorming a FinFET device structure 10 a, in accordance with someembodiments of the disclosure. FIGS. 2A-2E, 2F-2, 2G-2 showcross-sectional representations taken along line A-A in FIG. 1.

A substrate 102 is provided as shown in FIG. 1 in accordance with someembodiments. The substrate 102 may be a semiconductor wafer such as asilicon wafer. The substrate 102 may also include other elementarysemiconductor materials, compound semiconductor materials, and/or alloysemiconductor materials. Examples of the elementary semiconductormaterials may include, but are not limited to, crystal silicon,polycrystalline silicon, amorphous silicon, germanium, and/or diamond.Examples of the compound semiconductor materials may include, but arenot limited to, silicon carbide, gallium nitride, gallium arsenic,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide. Examples of the alloy semiconductor materials may include,but are not limited to, SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP,and/or GaInAsP. The substrate 102 may include an epitaxial layer. Forexample, the substrate 102 may have an epitaxial layer overlying a bulksemiconductor. In addition, the substrate 102 may also be semiconductoron insulator (SOI). The SOI substrate may be fabricated by a waferbonding process, a silicon film transfer process, a separation byimplantation of oxygen (SIMOX) process, other applicable methods, or acombination thereof. The substrate 102 may be an N-type substrate. Thesubstrate 102 may be a P-type substrate.

Next, as shown in FIG. 1, a doped region 104 is formed in the substrate102, in accordance with some embodiments. In some embodiments, the dopedregion 104 is an anti-punch-through (APT) region. The APT region may beused to offer greater protection against punch-through. As a result,current leakage caused by punch-through may be reduced or prevented.

In some embodiments, an ion implantation process is performed to dopethe substrate 102 with suitable dopants for forming the doped region104, as shown in FIG. 1. Since the ion implantation process for formingthe APT region may be performed before forming the fin structure, thesubsequently formed fin structure may be prevented from being damaged bythe ion implantation process. Therefore, device quality and reliabilitymay be improved.

In some embodiments, the concentration of dopants in the doped region104 is in a range from about 1E18 atoms/cm³ to about 1E19 atoms/cm³. Insome embodiments, the concentration of the dopants in the doped region104 is in a range from about 3E18 atoms/cm³ to about 1E20 atoms/cm³.Because the doped region 104 is formed before the formation of the finstructure, the concentration of dopants in the doped region 104 may beincreased without damaging the fin structure. The concentration ofdopants in the doped region 104 may be fine-tuned depending onrequirements. If the dopant concentration is too low, the currentleakage caused by punch-through may increase.

In some embodiments, the doped region 104 is a p-type doped region. Thedoped region 104 may be a portion of the substrate 102 doped with one ormore p-type dopants. For example, the p-type dopant may be boron. NMOSFinFET devices may be formed over the doped region 104.

In some embodiments, the doped region 104 is an n-type doped region. Thedoped region 104 may be a portion of the substrate 102 doped with one ormore n-type dopants. For example, the n-type dopant may be phosphor orarsenic. PMOS FinFET devices may be formed over the doped region 104.

Next, a pad layer may be blanketly formed over the substrate 102, and ahard mask layer may be blanketly formed over the pad layer (not shown).The pad layer may be a buffer layer between the substrate 102 and thehard mask layer. In addition, the pad layer may be used as a stop layerwhen the hard mask layer is removed. The pad layer may be made ofsilicon oxide. The hard mask layer may be made of silicon nitride,silicon oxide, silicon oxynitride, or another applicable material. Thepad layer and the hard mask layer may be formed by deposition processes,such as a chemical vapor deposition (CVD) process, a high-density plasmachemical vapor deposition (HDPCVD) process, a spin-on process, asputtering process, or another applicable process.

Afterwards, a photoresist layer may be formed over the hard mask layer(not shown). The photoresist layer may be patterned by a patterningprocess. The patterning process may include a photolithography processand an etching process. Examples of photolithography processes includephotoresist coating (e.g., spin-on coating), soft baking, mask aligning,exposure, post-exposure baking, developing the photoresist, rinsing anddrying (e.g., hard baking). The etching process may be a dry etchingprocess or a wet etching process. As a result, a patterned pad layer anda patterned hard mask layer may be obtained. Afterwards, the patternedphotoresist layer may be removed.

Afterwards, an etching process is performed on the substrate 102 to forma fin structure 106 by using the hard mask layer as a mask as shown inFIGS. 1 and 2A in accordance with some embodiments. The etching processmay be a dry etching process or a wet etching process. In someembodiments, the substrate 102 is etched by a dry etching process. Thedry etching process may include using a fluorine-based etchant gas, suchas SF₆, C_(x)F_(y) (where x and y may be positive integers), NF₃, or acombination thereof. The etching process may be a time-controlledprocess, and continue until the fin structure 106 reaches apredetermined height. As shown in FIGS. 1 and 2A, the bottom of the finstructure 106 is in the doped region 104. As shown in FIG. 2A, the finstructure has a width of W1.

Next, a liner layer 108 is conformally formed on the sidewalls and thetop surface of the fin structure 106 as shown in FIGS. 1 and 2A inaccordance with some embodiments. The liner layer 108 may preventsilicon in the fin structure 106 from being oxidized in the subsequentprocess for forming oxide over the liner layer 108. The liner layer 108may be used to protect the fin structure 106 from being damaged in thefollowing processes (such as an anneal process or an etching process).The liner layer 108 may be made of SiN, SiOx, SiON, SiCN, or acombination thereof. In some embodiments, the liner layer 108 has athickness in a range of about 3 Å to about 50 Å.

Next, an isolation layer 110 is formed to cover the fin structure 106and the substrate 102 as shown in FIGS. 1 and 2A in accordance with someembodiments. The isolation layer 110 may be made of silicon oxide,silicon nitride, silicon oxynitride, fluoride-doped silicate glass(FSG), or another low-k dielectric material. The isolation layer 110 maybe deposited by a deposition process, such as a chemical vapordeposition (CVD) process such as low pressure CVD (LPCVD), plasmaenhanced CVD (PECVD), or high density plasma CVD (HDP-CVD), high aspectratio process (HARP), flowable CVD (FCVD), atomic layer deposition(ALD), a spin-on-glass process, or another applicable process, or acombination thereof.

Afterwards, the isolation layer 110 may be planarized to expose the topsurface of the patterned hard mask layer (not shown). The isolationlayer 110 may be planarized by a chemical mechanical polishing (CMP)process. Afterwards, the patterned hard mask layer may be removed. Thepatterned hard mask layer may be removed by a wet etching process. Thewet etching process may include using a phosphoric acid (H₃PO₄) etchingsolution.

Next, an etching process is performed on the isolation layer 110, asshown in FIGS. 1 and 2A in accordance with some embodiments. The etchingprocess may be used to remove a portion of the liner layer and a portionof the isolation layer 110. As a result, the top portion of the finstructure 106 may be exposed and the remaining isolation layer 110 maysurround the base portion of the fin structure 106. The remainingisolation layer 110 may be an isolation structure 110 such as a shallowtrench isolation (STI) structure surrounding the bottom portion of thefin structure 106. In some embodiments as shown in FIGS. 1 and 2A, theisolation structure 110 surrounds the doped region 104 in the finstructure 106. The isolation structure 110 may be configured to preventelectrical interference or crosstalk.

Next, a cleaning process is performed on the fin structure 106, theliner layer 108, and the isolation structure 110, as shown in FIG. 2B inaccordance with some embodiments. The cleaning process may remove thenative oxide layer grown on the fin structure 106. The clean process maybe a wet cleaning process or a dry cleaning process. The wet cleaningprocess may use wet etching etchant such as hydrofluoric acid (HF). Thedry cleaning process may also include dry cleaning using etchant gassuch as SiF₆ with plasma, combination of plasma treated-NF₃/NH₃ orplasma treated-NF₃ and NH₃, or HF/NH₃ mixing gas.

In some embodiments, the liner layer 108 and the isolation structure 110are recessed by the cleaning process. In some embodiments as shown inFIG. 2B, the doped region 104 is exposed after the cleaning process. Insome embodiments as shown in FIG. 2B, the recessed height H1 of theliner layer 108 and the isolation structure 110 is in a range of about 6Å to about 80 Å. In some embodiments, the recessed height H1 of theliner layer 108 and the isolation structure 110 is in a range of about10 Å to about 60 Å. In some embodiments, the recessed height H1 of theliner layer 108 and the isolation structure 110 is in a range of about20 Å to about 50 Å. If the recessed height H1 of the liner layer 108 andthe isolation structure 110 is too great, the channel of FinFET devicestructure 10 a may include the doped region 104 and device performancemay degrade.

As shown in FIG. 2B, the fin structure 106 has a width of W2 after thecleaning process. In some embodiments, the width W1 of the fin structure106 before the cleaning process and the width W2 of the fin structure106 after the cleaning process are substantially the same. For example,the difference of the width W1 and the width W2 is in a range of about 3Å to about 50 Å.

Next, a cap layer 112 is formed over the fin structure 106 as shown inFIG. 2C in accordance with some embodiments. In some embodiments, thecap layer 112 and the fin structure 106 are made of the same material.Therefore, the cap layer 112 and the fin structure 106 may beindistinguishable since both of them are crystalline in nature. However,the boundary between the cap layer 112 and the fin structure 106 isstill shown by a dashed line for clarity. In some embodiments, the caplayer 112 is made of silicon.

In some embodiments as shown in FIG. 2C, the cap layer 112 isselectively grown over the sidewalls and the top surface of the finstructure 106. In some embodiments, the cap layer 112 is epitaxiallygrown. The cap layer 112 may be grown by a chemical vapor deposition(CVD) process such as a plasma-enhanced CVD (PECVD) process. Theprecursors such as silane (SiH₄), disilane (Si₂H₆), trisilane (Si₃H₈),dichlorosilane (SiH₂Cl₂), trichlorosilane (SiHCl₃), or othersilicon-containing precursors may be employed when growing the cap layer112. If the cap layer 112 is grown by CVD or PECVD, the cap layer 112may be grown under a temperature in a range of about 250° C. to about700° C. If the cap layer 112 is grown by CVD or PECVD, the cap layer 112may be grown under a pressure in a range of about 1 Torr to about 760Torr. If the temperature or the pressure is too high, the cap layer 112may be also grown over the isolation structure 110 and there may beleakage path in the cap layer 112 and the performance may be degraded.If the temperature or the pressure is too low, the cap layer 112 may notbe grown. As shown in FIG. 2C, the cap layer has a thickness T1.

The cap layer 112 may be grown by an atomic layer deposition (ALD)process such as a plasma-enhanced ALD (PEALD) process. The ALD processmay be performed by cyclic deposition including a self-limiting Simonolayer formation step and a hydrogen desorption step, for example. Ifthe cap layer 112 is grown by ALD or PEALD, the cap layer 112 may begrown under a temperature in a range of about 250° C. to about 600° C.If the cap layer 112 is grown by ALD or PEALD, the cap layer 112 may begrown under a pressure in a range of about 10 mTorr to about 700 mTorr.If the temperature or the pressure is too high, the cap layer 112 may bealso grown on the isolation structure 110 and there may be leakage pathin the cap layer 112 and the performance may be degraded. If thetemperature or the pressure is too low, the cap layer 112 may not begrown.

Next, a gate dielectric layer 114 a is conformally formed over andacross the fin structure 106, the liner layer 108, and the isolationstructure 110 as shown in FIG. 2D in accordance with some embodiments.The gate dielectric layer 114 a may be made of dielectric materials,such as silicon oxide, silicon nitride, silicon oxynitride, dielectricmaterial(s) with high dielectric constant (high-k), or a combinationthereof. In some embodiments, the gate dielectric layer is made ofsilicon oxide. The gate dielectric layer 114 a may be formed by adeposition process, such as chemical vapor deposition (CVD), physicalvapor deposition (PVD), atomic layer deposition (ALD), high densityplasma CVD (HDPCVD), metal organic CVD (MOCVD), or plasma enhanced CVD(PECVD).

As shown in FIG. 2D, the cap layer 112 has a thickness T2 after formingthe gate dielectric layer 114 a. In some embodiments, the thickness T2of the cap layer 112 after forming the gate dielectric layer 114 a is ina range of about 1 Å to about 30 Å. In some embodiments, the thicknessT2 of the cap layer 112 after forming the gate dielectric layer 114 a isin a range of about 2 Å to about 20 Å. In some embodiments, thethickness T2 of the cap layer 112 after forming the gate dielectriclayer 114 a is in a range of about 2 Å to about 8 Å. If the thickness T2of the cap layer 112 after forming the gate dielectric layer 114 a istoo thick, the device performance may degrade. If the thickness T2 ofthe cap layer 112 after forming the gate dielectric layer 114 a is toothin, the fin structure 106 may be damaged and there may be mechanicalintegrity issues or carrier mobility may degrade.

During the formation of the gate dielectric layer 114 a, the cap layer112 may be consumed or oxidized. In some embodiments, the thickness T1of the cap layer 112 before forming the gate dielectric layer 114 a isgreater than the thickness T2 of the cap layer 112 after forming thegate dielectric layer 114 a. In some embodiments, the difference betweenthe thickness T1 of the cap layer 112 and the thickness T2 of the caplayer 112 is less than 10 Å. In some embodiments, the difference betweenthe thickness T1 of the cap layer 112 and the thickness T2 of the caplayer 112 is less than 5 Å. In some embodiments, the difference betweenthe thickness T1 of the cap layer 112 and the thickness T2 of the caplayer 112 is less than 1 Å. If the difference between the thickness T1of the cap layer 112 and the thickness T2 of the cap layer 112 is toogreat, the cap layer 112 is consumed too much during the formation ofthe gate dielectric layer 114 a, therefore, the fin structure 106 may bedamaged and there may be mechanical integrity issues or carrier mobilitymay degrade.

It should be noted that although in FIG. 2D the sidewall of the caplayer 112 is aligned with the sidewall of the liner layer 108. Thesidewall of the cap layer 112 may also be misaligned with the sidewallof the liner layer 108.

In some embodiments, since the cap layer 112 and the fin structure 106are made of the same material, the cap layer 112 and the fin structure106 is be indistinguishable. Therefore, as shown in FIG. 2E, afterforming the gate dielectric layer 114 a, the fin structure 106 includesa bottom portion 106B, a middle portion 106M, and top portion 106T. Insome embodiments, the bottom portion 106B and the middle portion 106M ofthe fin structure 106 are in the doped region 104 and are doped with afirst dopant concentration. In some embodiments, the top portion 106T ofthe fin structure 106 is doped with a second dopant concentration orundoped. In some embodiments, the first dopant concentration is higherthan the second dopant concentration.

It should be noted that, there is no obvious interface between thebottom portion 106B, the middle portion 106M, and the top portion 106Tof the fin structure 106, and therefore the interface between them isshown by a dashed line.

As shown in FIG. 2E, compared to the bottom portion 106B of the finstructure 106, the middle portion 106M of the fin structure 106laterally protrudes from a sidewall of the middle portion 106M of thefin structure 106. In some embodiments, the middle portion 106M has aprotruding portion 106P of the fin structure 106 laterally extendingover the liner layer 108. In some embodiments, the protruding portion106P of the fin structure 106 is in direct contact with the top surfaceof the liner layer 108.

As shown in FIG. 2E, the top portion 106T of the fin structure 106 andthe middle portion 106M of the fin structure 106 has a width of WT, andthe bottom portion 106B of the fin structure 106 has a width of WB. Insome embodiments, since the middle portion 106M of the fin structurelaterally protrudes over the liner layer 108, the width WT of the topportion 106T and the middle portion 106M of the fin structure 106 iswider than the width WB of the bottom portion 106B of the fin structure106.

As shown in FIGS. 2D and 2E, after forming the gate dielectric layer 114a, the cap layer 112 remains over the fin structure 106. Therefore, thefin structure 106 may not be damaged during the formation of the gatedielectric layer 114 a, and mechanical integrity issues or carriermobility degradation may be prevented.

Next, a dummy gate layer may be conformally formed over the gatedielectric layer 114 a (not shown). The dummy gate layer may be made ofpolysilicon. The dummy gate layer may be formed by a deposition process,such as chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD),metal organic CVD (MOCVD), or plasma enhanced CVD (PECVD).

Afterwards, an etching process may be performed on the dummy gate layerto form a dummy gate structure by using a patterned photoresist layer asa mask (not shown). The dummy oxide layer may also be partially removedin the etching process. The etching process may be a dry etching processor a wet etching process. In some embodiments, the dummy gate layer andthe dummy oxide layer are etched by a dry etching process. The dryetching process may include using a fluorine-based etchant gas, such asSF₆, C_(x)F_(y) (where x and y may be positive integers), NF₃, or acombination thereof. After the etching process, the top portion of thefin structure 106 may be exposed on the opposite sides of the dummy gatestructure.

Next, as shown in FIG. 2F-1 in accordance with some embodiments, a pairof spacers 116 are formed on opposite sidewalls of the dummy gatestructure. The spacers 116 may be made of silicon oxide, siliconnitride, silicon oxynitride, and/or dielectric materials. The spacers116 may be formed by a chemical vapor deposition (CVD) process, aspin-on-glass process, or another applicable process.

Afterwards, the top portion of the fin structure 106 exposed on theopposite sides of the dummy gate structure is removed to form a recessby an etching process (not shown). The etching process may include a dryetching process or a wet etching process. In some embodiments, the finstructure 106 is etched by a dry etching process. The dry etchingprocess may include using a fluorine-based etchant gas, such as SF₆,C_(x)F_(y) (where x and y may be positive integers), NF₃, or acombination thereof.

Next, as shown in FIG. 2F-1 in accordance with some embodiments, asource/drain (S/D) structure 118 are formed in the recess over the finstructure 106. A strained material may be grown in the recess by anepitaxial (epi) process to form the S/D structure 118. In addition, thelattice constant of the strained material may be different from thelattice constant of the substrate 102. The S/D structure 118 may includeGe, SiGe, InAs, InGaAs, InSb, GaAs, GaSb, InAlP, InP, SiC, SiP, otherapplicable materials, or a combination thereof. The S/D structure 118may be formed by an epitaxial growth step, such as metalorganic chemicalvapor deposition (MOCVD), metalorganic vapor phase epitaxy (MOVPE),plasma-enhanced chemical vapor deposition (PECVD), remoteplasma-enhanced chemical vapor deposition (RP-CVD), molecular beamepitaxy (MBE), hydride vapor phase epitaxy (HYPE), liquid phase epitaxy(LPE), chloride vapor phase epitaxy (Cl-VPE), or any other suitablemethod.

After the S/D structure 118 is formed, as shown in FIG. 2F-1 inaccordance with some embodiments, an inter-layer dielectric (ILD)structure 120 is formed to cover the S/D structure 118. The inter-layerdielectric structure 120 may include multilayers made of multipledielectric materials, such as silicon oxide, silicon nitride, siliconoxynitride, phosphosilicate glass (PSG), borophosphosilicate glass(BPSG), low-k dielectric material, and/or other applicable dielectricmaterials. Examples of low-k dielectric materials include, but are notlimited to, fluorinated silica glass (FSG), carbon doped silicon oxide,amorphous fluorinated carbon, parylene, bis-benzocyclobutenes (BCB), orpolyimide. The inter-layer dielectric structure 120 may be formed bychemical vapor deposition (CVD), spin-on coating, or other applicableprocesses.

Afterwards, a planarizing process is performed on the ILD structure 120until the top surface of the dummy gate structure is exposed (notshown). After the planarizing process, the top surface of the dummy gatestructure may be substantially level with the top surfaces of thespacers 116 and the ILD structure 120. The planarizing process mayinclude a grinding process, a chemical mechanical polishing (CMP)process, an etching process, another applicable process, or acombination thereof.

Next, the dummy gate structure is removed to form a trench between thespacers 116 (not shown). The fin structure 106 may be exposed from thetrench. The dummy gate structure may be removed by an etching process,such as a dry etching process or a wet etching process.

FIG. 2F-2 shows a cross-sectional representation taken along line 2-2 inFIG. 2F-1. Next, as shown in FIGS. 2F-1 and 2F-2 in accordance with someembodiments, a gate structure 122 a is formed over the gate dielectriclayer 114 a across the fin structure 106. As shown in FIGS. 2F-1 and2F-2, the gate structure 122 a includes a gate dielectric layer 114 a, awork function layer 124 a, and a gate electrode layer 126.

As shown in FIGS. 2F-1 and 2F-2, the work function layer 124 a is formedover the gate dielectric layer 114 a. The work function layer 124 a mayprovide the desired work function for transistors to enhance deviceperformance including improved threshold voltage. The work functionlayer 124 a may be made of metal materials, and the metal materials mayinclude N-work-function metal or P-work-function metal. For N-typetransistors, N-work-function metal may include tungsten (W), copper(Cu), titanium (Ti), silver (Ag), aluminum (Al), titanium aluminum alloy(TiAl), titanium aluminum nitride (TiAlN), tantalum carbide (TaC),tantalum carbon nitride (TaCN), tantalum silicon nitride (TaSiN),manganese (Mn), zirconium (Zr), or a combination thereof. For P-typetransistors, the P-work-function metal may include titanium nitride(TiN), tungsten nitride (WN), tantalum nitride (TaN), ruthenium (Ru) ora combination thereof.

As shown in FIGS. 2F-1 and 2F-2, the gate electrode layer 126 is formedover the work function layer 124 a. The metal gate electrode layer 126may be made of a conductive material, such as aluminum, copper,tungsten, titanium, tantalum, titanium nitride, tantalum nitride, nickelsilicide, cobalt silicide, TaC, TaSiN, TaCN, TiAl, TiAlN, or otherapplicable materials. The gate electrode layer 126 may be formed by achemical vapor deposition process (e.g., a low pressure chemical vapordeposition process, or a plasma enhanced chemical vapor depositionprocess), a physical vapor deposition process (e.g., a vacuumevaporation process, or a sputtering process), other applicableprocesses, or a combination thereof.

Next, a second ILD structure 128 is blanketly formed over the first ILDstructure 120 and the gate structure 122 a, as shown in FIGS. 2G-1 and2G-2 in accordance with some embodiments. The processes for forming thesecond ILD structure 128 may be the same as, or similar to, those usedto form the first ILD structure 120. For the purpose of brevity, thedescriptions of these processes are not repeated herein.

Next, a portion of the second ILD structure 128 over the gate structure122 a may be removed, and a trench may be formed over gate structure 122a (not shown). The trench may be formed by an etching process such as adry etching process or a wet etching process. The gate structure 122 amay be exposed from the trenches.

Afterwards, a contact structure 130 is filled into the trench, as shownin FIGS. 2G-1 and 2G-2 in accordance with some embodiments. The contactstructure 130 may be made of metal materials (e.g., W, Al, or Cu), metalalloys, poly-Si, other applicable conductive materials, or a combinationthereof. The contact structure 130 can be formed by using a chemicalvapor deposition process (CVD), a physical vapor deposition process(PVD, e.g., evaporation or sputter), an atomic layer deposition process(ALD), an electroplating process, another suitable process, or acombination thereof to deposit the conductive materials of the firstcontact structure, and then optionally performing a chemical mechanicalpolishing (CMP) process or an etching back process to remove excessconductive materials. In some embodiments, the contact structure 130electrically connected to the gate structure 122 a underneath.

By selectively growing a cap layer 112 over the fin structure 106 beforeforming the gate dielectric layer 114 a, the fin structure 106 may notbe consumed during the formation of the gate dielectric layer 114 a, andmechanical integrity issues or carrier mobility degradation may beprevented.

Many variations and/or modifications may be made to the embodiments ofthe disclosure. FIGS. 3A-3G are cross-sectional representations ofvarious stages of forming a FinFET device structure 10 b, in accordancewith some embodiments of the disclosure. Some processes or devices arethe same as, or similar to, those described in the embodiments above,and therefore the descriptions of these processes and devices are notrepeated herein. The difference from the embodiments described above isthat, as shown in FIG. 3B in accordance with some embodiments, the finstructure 106 is trimmed after forming the fin structure 106.

In some embodiments as shown in FIGS. 3A and 3B, the top portion of thefin structure 106 has a fin width W1 b after forming the fin structure106 and a fin width W2 b of the fin structure 106 after trimming the finstructure 106. The fin width W2 b of the top portion of the finstructure 106 after trimming the fin structure 106 is narrower than thefin width W1 b before trimming the fin structure 106. As shown in FIG.3B, the fin width W1 b of the bottom portion of the fin structure 106remains after trimming the fin structure 106. In some embodiments, thefin width W1 b of the bottom portion of the fin structure 106 is widerthan the fin width W2 b of the top portion of the fin structure 106after trimming the fin structure 106.

In some embodiments as shown in FIG. 3B, the liner layer 108 and theisolation structure 110 are vertically recessed by a height H2. In someembodiments, the recess height H2 is in a range of about 3 Å to about 30Å.

The trimming process may remove the by-product of the process formingthe fin structure 106. The trimming process may also enhance the deviceperformance. The trimming may include a wet etching process or a dryetching process. The wet cleaning process may use wet etching etchantsuch as hydrofluoric acid (HF). The dry cleaning process may alsoinclude dry cleaning using etchant gas such as SiF₆ with plasma,combination of plasma treated-NF₃/NH₃ or plasma treated-NF₃ and NH₃, orHF/NH₃ mixing gas.

Next, a cleaning process is performed over the fin structure 106 asshown in FIG. 3C in accordance with some embodiments. The cleaningprocess may be the same as, or similar to, the process performed in theembodiment as shown in FIG. 2B. For the purpose of brevity, thedescriptions of these processes are not repeated herein.

As shown in FIG. 3C, the cleaning process further recess the liner layer108 and the isolation structure 110 by a height H1. Therefore, the finstructure 106 has a protruding portion 106P adjacent to the top surfaceof the liner layer 108 and the isolation structure 110.

Next, as shown in FIG. 3D, a cap layer 112 is conformally grown over thefin structure 106. In some embodiments, the cap layer 112 covers the topsurface and the sidewall of the protruding portion 106P of the finstructure 106 and the top surface of the liner layer 108. As shown inFIG. 3D, the cap layer 112 further laterally extend from the sidewall ofthe protruding portion 106P of the fin structure 106. The material andthe process of growing the cap layer 112 may be the same as, or similarto, those in the embodiment as shown in FIG. 2C. For the purpose ofbrevity, the descriptions of these materials and the processes are notrepeated herein.

Afterwards, as shown in FIG. 3E, a gate dielectric layer 114 a is formedover the cap layer 112, the liner layer 108, and the isolation structure110 as shown in FIG. 3E in accordance with some embodiments. Thematerial and the process of growing the cap layer 112 may be the sameas, or similar to, the process performed in the embodiment as shown inFIG. 2D. For the purpose of brevity, the descriptions of the materialsand the processes are not repeated herein. Since the fin structure 106is trimmed and the liner layer 108 and the isolation structure 110 isrecess, the doped region 104 in the fin structure 106 has a narrower topportion 104T as shown in FIG. 3E.

In some embodiments, since the cap layer 112 and the fin structure 106are made of the same material, the cap layer 112 and the fin structure106 are indistinguishable. Therefore, as shown in FIG. 3F, after formingthe gate dielectric layer 114 a, the fin structure 106 includes a bottomportion 106B, a middle portion 106M including the protruding portion106P, and the top portion 106T.

As shown in FIG. 3F, compared to the bottom portion 106B of the finstructure 106, the middle portion 106B including the protruding portion106P of the fin structure 106 laterally protrudes from a sidewall of themiddle portion 106M of the fin structure 106. As shown in FIG. 3F, theprotrusion I is the lateral distance between a sidewall of the middleportion 106M of the fin structure 106 and a sidewall of the bottomportion 106B of the fin structure. In some embodiments as shown in FIG.3F, the protrusion I is in a range from about 2 Å to about 30 Å. In someembodiments, the protrusion I is in a range from about 2 Å to about 20Å. In some embodiments, the protrusion I is in a range from about 2 Å toabout 8 Å. If the protrusion I is too great, the fin structure 106 maybe too wide, and the device performance may degrade. If the protrusion Iis too less, the cap layer 112 may be too thin, and the fin structure106 may be consumed during the formation of the gate dielectric layer114 a.

As shown in FIG. 3F, the top portion 106T of the fin structure 106 has awidth of WTb, the middle portion 106M of the fin structure 106 has awidth of WMb, and the bottom portion 106B of the fin structure 106 has awidth of WBb. In some embodiments, since the middle portion 106M of thefin structure laterally protrudes over the liner layer 108 and the finstructure 106 is trimmed, the width WMb of the middle portion 106M ofthe fin structure 106 is wider than the width WTb of the top portion106T of the fin structure 106. In addition, as shown in FIG. 3F, thewidth WMb of the middle portion 106M of the fin structure 106 is widerthan the width WBb of the bottom portion 106B of the fin structure 106.

Next, as shown in FIG. 3G, a gate structure 122 a is formed over thegate dielectric layer 114 a, and a second ILD structure 128 is formedover the gate structure 122 a. Moreover, a contact structure 130 isformed in the second ILD structure 128 electrically connected to thegate structure 122 a. The material and the process of forming the gatestructure 122 a, the second ILD structure 128, and the contact structure130 may be the same as, or similar to, the process performed in theembodiment as shown in FIGS. 2F-1, 2F-2, 2G-1, and 2G-2. For the purposeof brevity, the descriptions of these processes are not repeated herein.

By selectively growing a cap layer 112 over the fin structure 106 beforeforming the gate dielectric layer 114 a, the fin structure 106 may notbe consumed during the formation of the gate dielectric layer 114 a, andmechanical integrity issues or carrier mobility degradation may beprevented. In addition, trimming the fin structure 106 after forming thefin structure 106 may remove the by-product of previous process.Moreover, the device performance may be also enhanced.

Many variations and/or modifications may be made to the embodiments ofthe disclosure. FIGS. 4A-4C are cross-sectional representations ofvarious stages of forming a FinFET device structure 10 c, in accordancewith some embodiments of the disclosure. Some processes or devices arethe same as, or similar to, those described in the embodiments above,and therefore the descriptions of these processes and devices are notrepeated herein. The difference from the embodiments described above isthat, as shown in FIG. 4A, the cap layer 112 is also grown over theisolation structure 110.

In some embodiments, the cap layer 112 is non-selectively grown over thefin structure 106, the liner layer 108, and the isolation structure 110.In some embodiments, the cap layer 112 formed over the liner layer 108and the isolation structure 110 is an amorphous portion 112 a, and thecap layer 112 formed over the fin structure 106 is a crystallizedportion 112 c. As shown in FIG. 4A, the amorphous portion 112 a of thecap layer 112 is in direct contact with the crystallized portion 112 cof the cap layer 112 over the fin structure 106. In some embodiments,the amorphous portion 112 a of the cap layer 112 is also in directcontact with the liner layer 108 and the isolation structure 106.

In some embodiments, if the cap layer 112 is grown by CVD or PECVD, thecap layer 112 may be grown under a temperature above about 700° C. andunder a pressure above 760 Torr. In some embodiments, if the cap layer112 is grown by ALD or PEALD, the cap layer 112 may be grown under atemperature above about 600° C. and under a pressure above 700 mTorr. Insome embodiments, the precursor of the deposition process of the caplayer 112 includes high order silane such as Si₂H₆ or Si₃H₈. Under theseprocessing conditions, the cap layer 112 may be also grown over theliner layer 108 and the isolation structure 110. Since the isolationstructure 110 may be a dielectric material, the cap layer 112 grown overthe isolation structure 110 may be amorphous. Since the native oxidelayer formed over the cap layer 112 may be removed during the cleaningprocess, the cap layer 112 grown over the fin structure 106 may becrystallized.

Next, as shown in FIG. 4B, the gate dielectric layer 114 a is formedover the cap layer 106, including the amorphous portion 112 a over theisolation structure 110 and the crystallized portion 112 c over the finstructure 106. During formation of the gate dielectric layer 114 a, theamorphous portion 112 a of the cap layer 112 may be consumed oroxidized. The remaining amorphous portion 112 a of the cap layer 112after forming of the gate dielectric layer 114 a may be re-crystallizedto poly-crystalline due to thermal treatment of the formation of thegate dielectric layer 114 a. Therefore, a poly-crystalline portion 112 pis formed covering the liner layer 108 and partially covering theisolation structure 110. In some embodiments, the poly-crystallineportion 112 p of the cap layer 112 is made of poly-crystalline silicon.

As shown in FIG. 4B, compared to the bottom portion of the fin structure106, the poly-crystalline portion 112 p of the cap layer 112 laterallyprotrudes from a sidewall of the fin structure 106 by a protrusion Ic.In some embodiments as shown in FIG. 4B, the protrusion Ic of theprotruding portion 112 p is in a range from about 2 Å to about 30 Å. Insome embodiments, the protrusion Ic of the protruding portion 112 p isin a range from about 2 Å to about 20 Å. In some embodiments, theprotrusion Ic of the protruding portion 112 p is in a range from about 2Å to about 8 Å. If the protrusion Ic is too great, the fin structure 106may be too wide, and the device performance may degrade. If theprotrusion Ic is too less, the cap layer 112 may be too thin, and thefin structure 106 may be consumed during the formation of the gatedielectric layer 114 a.

Next, as shown in FIG. 4C, a gate structure 122 a is formed over thegate dielectric layer 114 a, and a second ILD structure 128 is formedover the gate structure 122 a. Moreover, a contact structure 130 isformed in the second ILD structure 128. The material and the process offorming the gate structure 122 a, the second ILD structure 128, and thecontact structure 130 may be the same as, or similar to, the processperformed in the embodiment as shown in FIGS. 2F-1, 2F-2, 2G-1, and2G-2. For the purpose of brevity, the descriptions of these processesare not repeated herein.

By growing a cap layer 112 over the fin structure 106 before forming thegate dielectric layer 114 a, the fin structure 106 may not be consumedduring the formation of the gate dielectric layer 114 a, and mechanicalintegrity issues or carrier mobility degradation may be prevented.Trimming the fin structure 106 is after forming the fin structure 106may remove the by-product of previous process. The device performancemay be also enhanced. In addition, since the cap layer 112 isnon-selectively grown over the fin structure 106, the liner layer 108,and the isolation structure 110, the cap layer 112 may has apoly-crystalline protruding portion 112 p laterally extending over theliner layer 108, which may help to identify the cap layer process withless fin structure 106 damage.

Many variations and/or modifications may be made to the embodiments ofthe disclosure. FIGS. 5A-5F are cross-sectional representations ofvarious stages of forming a FinFET device structure 10 d, in accordancewith some embodiments of the disclosure. Some processes or devices arethe same as, or similar to, those described in the embodiments above,and therefore the descriptions of these processes and devices are notrepeated herein. The difference from the embodiments described above isthat, as shown in FIG. 5B, after trimming the fin structure 106, the finstructure 106 adjacent to the top surface of the isolation structure 110has a curved sidewall 106S.

In some embodiments as shown in FIG. 5B, the liner layer 108 and theisolation structure 110 are recessed by a height H2. As shown in FIG.5B, a portion of the doped region 104 of the fin structure 106 isexposed, which has a curved sidewall 106S.

Next, as shown in FIG. 5C, after the cleaning process, the liner layer108 and the isolation structure 110 are further recessed by a height H1.As shown in FIG. 5C, a portion of the doped region 104 of the finstructure 106 is further exposed, which has a straight sidewall and acurved top surface 106S.

Afterwards, as shown in FIGS. 5D and 5E, the cap layer 112 isselectively grown over the fin structure 106 and the gate dielectriclayer 114 a is deposited over the cap layer 112. As shown in FIG. 5E,the fin structure 106 has a protruding portion 106P at the middle of thefin structure 106. In some embodiments, the protruding portion 106P atthe middle portion of the fin structure 106 which has a curved topsurface 106S and a straight sidewall is above the top surface of theliner layer 108.

Next, as shown in FIG. 5F, a gate structure 122 a is formed over thegate dielectric layer 114 a, and a second ILD structure 128 is formedover the gate structure 122 a. Moreover, a contact structure 130 isformed in the second ILD structure 128. The material and the process offorming the gate structure 122 a, the second ILD structure 128, and thecontact structure 130 may be the same as, or similar to, the processperformed in the embodiment as shown in FIGS. 2F-1, 2F-2, 2G-1, and2G-2. For the purpose of brevity, the descriptions of these processesare not repeated herein.

By selectively growing a silicon cap layer 112 over the fin structure106 before forming the gate dielectric layer 114 a, the fin structure106 may not be consumed during the formation of the gate dielectriclayer 114 a, and mechanical integrity issues or carrier mobilitydegradation may be prevented. In addition, trimming the fin structure106 after forming the fin structure 106 may remove the by-product ofprevious process. Moreover, the device performance may be also enhanced.Trimming the fin structure 106 may cause a protruding portion 106P ofthe fin structure 106 with a curved top surface 106S, which isrecognizable in the final structure.

Many variations and/or modifications may be made to the embodiments ofthe disclosure. FIGS. 6A-6C are cross-sectional representations ofvarious stages of forming a FinFET device structure 10 e, in accordancewith some embodiments of the disclosure. Some processes or devices arethe same as, or similar to, those described in the embodiments above,and therefore the descriptions of these processes and devices are notrepeated herein. The difference from the embodiments described above isthat, as shown in FIG. 6A, after trimming the fin structure 106, the finstructure 106 adjacent to the top surface of the isolation structure 110has a curved sidewall 106S, and the cap layer 112 is also grown over theisolation structure 110.

In some embodiments as shown in FIGS. 6A and 6B, the cap layer 112includes an amorphous portion 112 a covering the liner layer 108 and theisolation structure 110. The cap layer 112 also includes a crystallizedportion 112 c covering the fin structure 106. After forming the gatedielectric layer 114 a, the amorphous portion 112 a of the cap layer 112may re-crystallized to a poly-crystalline portion 112 p covering theliner layer 108 and the isolation structure 110. As shown in FIG. 6B,the crystallized portion 112 c of the cap layer 112 covers theprotruding portion 106P of the fin structure 106 (i.e., the top portionof the doped region 104 of the fin structure 106), which has a curvedtop surface at the corner.

Next, as shown in FIG. 6C, a gate structure 122 a is formed over thegate dielectric layer 114 a, and a second ILD structure 128 is formedover the gate structure 122 a. Moreover, a contact structure 130 isformed in the second ILD structure 128. The material and the process offorming the gate structure 122 a, the second ILD structure 128, and thecontact structure 130 may be the same as, or similar to, the processperformed in the embodiment as shown in FIGS. 2F-1, 2F-2, 2G-1, and2G-2. For the purpose of brevity, the descriptions of these processesare not repeated herein.

By growing a cap layer 112 over the fin structure 106 before forming thegate dielectric layer 114 a, the fin structure 106 may not be consumedduring the formation of the gate dielectric layer 114 a, and mechanicalintegrity issues or carrier mobility degradation may be prevented.Trimming the fin structure 106 is after forming the fin structure 106may remove the by-product of previous process. The device performancemay be also enhanced. In addition, since the cap layer 112 isnon-selectively grown over the fin structure 106, the liner layer 108,and the isolation structure 110, the cap layer 112 may has apoly-crystalline protruding portion 112 p laterally extending over theliner layer 108, which may help to identify the cap layer process withless fin structure 106 damage. Trimming the fin structure 106 may causea protruding portion 106P with a curved top surface 106S, which isrecognizable in the final structure.

FIG. 7 is a cross-sectional representation of the FinFET devicestructure 10 a, in accordance with some embodiments of the disclosure.FIG. 7 shows a cross-sectional representation taken along line 7-7 inFIG. 2F-1.

In some embodiments as shown in FIG. 7, After growing the cap layer 112,since the cap layer 112 and the fin structure 106 may beindistinguishable since both of them are crystalline in nature, themiddle portion 106M of the fin structure 106 laterally protrudes byprotrusion I. If the protrusion I is too great, device performance maydegrade. If the protrusion I is too less, there may be etching loss insubsequently process.

As shown in FIG. 7, the middle portion 106M of the fin structure 106covers the liner layer 108. Afterwards, the S/D structure 118 may beformed over the middle portion 106M of the fin structure 106 (i.e. thecap layer 112) adjacent to the isolation structure 110.

By growing a cap layer 112 over the fin structure 106 before forming thegate dielectric layer 114 a, the fin structure 106 may not be consumedduring the formation of the gate dielectric layer 114 a, and mechanicalintegrity issues or carrier mobility degradation may be prevented. Inaddition, the cap layer 112 may form a protruding portion adjacent tothe isolation structure 110 and the S/D structure 118 may be formed overthe protruding portion, which may prevent etching loss.

Many variations and/or modifications may be made to the embodiments ofthe disclosure. FIGS. 8A-8B are cross-sectional representations ofvarious stages of forming a FinFET device structure 10 f, in accordancewith some embodiments of the disclosure. Some processes or devices arethe same as, or similar to, those described in the embodiments above,and therefore the descriptions of these processes and devices are notrepeated herein. The difference from the embodiments described above isthat, as shown in FIG. 8A, the gate dielectric layer 114 a is removedafter the removal of the dummy gate layer.

After the gate dielectric layer 114 a is removed, the liner layer 108and the isolation structure 110 are further vertically recessed.Therefore, the middle portion 106M of the fin structure 106 which has aprotruding portion 106P protrudes from the sidewall is separated fromthe liner layer 108 and the fin structure 110.

Next, as shown in FIG. 8A, an interfacial layer 132 is conformallyformed over the fin structure 106. The interfacial layer 132 may includesilicon oxide. The silicon oxide may be formed by an oxidation process(such as a dry oxidation process, or a wet oxidation process), adeposition process (such as a chemical vapor deposition (CVD) process oran atomic layer deposition (ALD) process), other applicable processes,or a combination thereof. The interfacial layer 132 may be thermallygrown using a thermal oxidation process in oxygen-containing ambient ornitrogen-containing ambient (e.g. NO or N₂O).

Next, as shown in FIG. 8A, a gate dielectric layer 114 b may be formedover the interfacial layer 132, the liner layer 108, and the isolationstructure 110. The gate dielectric layer 114 b may include a high-kdielectric layer (e.g., the dielectric constant is greater than 3.9)such as hafnium oxide (HfO₂). Alternatively, the high-k dielectric layermay include other high-k dielectrics, such as LaO, AlO, ZrO, TiO, Ta₂O₅,Y₂O₃, SrTiO₃, BaTiO₃, BaZrO, HfZrO, HfLaO, HfTaO, HfSiO, HfSiON, HfTiO,LaSiO, AlSiO, (Ba, Sr)TiO₃, Al₂O₃, other applicable high-k dielectricmaterials, or a combination thereof. The high-k dielectric layer may beformed by a chemical vapor deposition process (e.g., a plasma enhancedchemical vapor deposition (PECVD) process, or a metalorganic chemicalvapor deposition (MOCVD) process), an atomic layer deposition (ALD)process (e.g., a plasma enhanced atomic layer deposition (PEALD)process), a physical vapor deposition (PVD) process (e.g., a vacuumevaporation process, or a sputtering process), other applicableprocesses, or a combination thereof.

In some embodiments as shown in FIG. 8A, since the protruding portion106P of the fin structure 106 is separated from the liner layer 108 andthe fin structure 106, the interfacial layer 132 and the gate dielectriclayer 114 b are sandwiched between the protruding portion 106P and theliner layer 108 and the isolation structure 110.

Next, as shown in FIG. 8B, a work function layer 124 b is formed overthe gate dielectric layer 114 b. The material and the process of formingthe work function layer 124 b may be the same as, or similar to, thematerial and the process performed in the embodiment as shown in FIGS.2F-1 and 2F-2. For the purpose of brevity, the descriptions of theseprocesses are not repeated herein. However, it should be noted that, dueto different demand of threshold voltage, the material or the thicknessof work function layer 124 b may be different from those of the workfunction layer 124 a in the embodiment as shown in FIGS. 2F-1 and 2F-2.

Afterwards, the gate electrode layer 126 is formed over the workfunction layer 124 b, and a gate structure 122 b including theinterfacial layer 132, the gate dielectric layer 114 b, the workfunction layer 124 b, and the gate electrode layer 126 may be formed, inthe embodiment as shown in FIG. 8B. Next, a second ILD structure 128 isformed over the gate structure 122 b, and a contact structure 130 isformed in the second ILD structure 128. The material and the process offorming the gate electrode layer 126, the second ILD structure 128, andthe contact structure 130 may be the same as, or similar to, the processperformed in the embodiment as shown in FIGS. 2F-1, 2F-2, 2G-1, and2G-2. For the purpose of brevity, the descriptions of these processesare not repeated herein.

In some embodiments, the FinFET device structure 10 f with gatestructure 122 b and the FinFET device structure 10 a with gate structure122 a are formed at different region. For example, the FinFET devicestructure 10 f with gate structure 122 b may be a device in a coreregion, and the FinFET device structure l0 a with gate structure 122 amay be a device in an input/output (I/O) region.

By selectively growing a silicon cap layer 112 over the fin structure106 before forming the gate dielectric layer 114 b, the fin structure106 may not be consumed during the formation of the gate dielectriclayer 114 a, and mechanical integrity issues or carrier mobilitydegradation may be prevented. In addition, the protruding portion 106Pof the cap layer 106 is separated from the liner layer 108 and theisolation structure 110, which may help to identify the cap layerprocess with less fin structure 106 damage.

As described previously, a cap layer 106 is grown before forming thegate dielectric layer 114 a or 114 b, the fin structure 106 may not beconsumed during the formation of the gate dielectric layer 114 a or 114b. The cap layer 112 may form a protruding portion 106P of the finstructure 106, which may help to identify the cap layer process. The caplayer 106 may be selectively or non-selectively grown over the finstructure 106 with different protruding portion 106P sidewall profiles,and may be applied to devices in both I/O and core region.

Embodiments of a method for forming a FinFET device structure areprovided. The method for forming the FinFET device structure may includegrowing a cap layer over the fin structure before forming the gatedielectric layer. The fin structure may not be consumed, and themechanical integrity issues or carrier mobility degradation may beprevented. A laterally protruding portion of the cap layer may help toidentify the process with less fin structure damage.

In some embodiments, a method for forming a fin field effect transistordevice structure is provided. The method for forming a fin field effecttransistor device structure includes forming a fin structure over asubstrate. The method for forming a fin field effect transistor devicestructure also includes forming an isolation structure surrounding thefin structure. The method for forming a fin field effect transistordevice structure also includes cleaning sidewalls of the fin structure.The method for forming a fin field effect transistor device structurealso includes depositing a silicon cap layer over the fin structure. Themethod for forming a fin field effect transistor device structure alsoincludes growing an oxide layer over the silicon cap layer. The siliconcap layer is thinned after growing an oxide layer over the silicon caplayer. The method for forming a fin field effect transistor devicestructure also includes forming a gate structure over the oxide layeracross the fin structure. The method for forming a fin field effecttransistor device structure also includes growing a source/drainepitaxial structure beside the gate structure. The method for forming afin field effect transistor device structure also includes forming acontact structure electrically connected to the gate structure.

In some embodiments, a method for forming a fin field effect transistordevice structure is provided. The method for forming a fin field effecttransistor device structure includes forming a fin structure protrudingfrom a substrate. The method for forming a fin field effect transistordevice structure also includes forming a liner layer and an isolationstructure surrounding the fin structure. The method for forming a finfield effect transistor device structure also includes recessing theliner layer and the isolation structure. The method for forming a finfield effect transistor device structure also includes growing a caplayer covering the fin structure. The method for forming a fin fieldeffect transistor device structure also includes forming a first gatedielectric layer covering the cap layer, the liner layer, and theisolation structure. A portion of the cap layer is consumed. The methodfor forming a fin field effect transistor device structure also includesforming a gate structure over the first gate dielectric layer across thefin structure. The method for forming a fin field effect transistordevice structure also includes growing source/drain epitaxial structureson opposite sides of the gate structure. The method for forming a finfield effect transistor device structure also includes forming a contactstructure over the gate structure.

In some embodiments, a fin field effect transistor device structure isprovided. The fin field effect transistor device structure includes afin structure formed over a substrate. The fin field effect transistordevice structure also includes a liner layer and an isolation structuresurrounding the fin structure. The fin field effect transistor devicestructure also includes a gate dielectric layer formed over the finstructure and the isolation structure. The fin field effect transistordevice structure also includes a gate structure formed over the gatedielectric layer. The fin field effect transistor device structure alsoincludes source/drain epitaxial structures formed on opposite sides ofthe gate structure. The fin structure comprises a protruding portionlaterally extending over the liner layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a fin field effecttransistor device structure, comprising: forming a fin structure over asubstrate; forming an isolation structure surrounding the fin structure;cleaning sidewalls of the fin structure; depositing a silicon cap layerover the fin structure; growing an oxide layer over the silicon caplayer, wherein the silicon cap layer is thinned after growing an oxidelayer over the silicon cap layer; forming a gate structure over theoxide layer across the fin structure; growing a source/drain epitaxialstructure beside the gate structure; and forming a contact structureelectrically connected to the gate structure, wherein the silicon caplayer and the fin structure are made of the same material.
 2. The methodfor forming the fin field effect transistor device structure as claimedin claim 1, further comprising: trimming the fin structure to narrow thefin structure, wherein the isolation structure is vertically recessedafter trimming the fin structure.
 3. The method for forming the finfield effect transistor device structure as claimed in claim 2, whereinafter trimming the fin structure, the fin structure has a curvedsidewall adjacent to the top surface of the isolation structure.
 4. Themethod for forming the fin field effect transistor device structure asclaimed in claim 1, wherein after cleaning the sidewalls of the finstructure, the fin structure has a protruding portion adjacent to thetop surface of the isolation structure.
 5. The method for forming thefin field effect transistor device structure as claimed in claim 1,further comprising: forming an amorphous portion of the silicon caplayer over the isolation structure, wherein the amorphous portion of thesilicon cap layer is in contact with the silicon cap layer over the finstructure.
 6. The method for forming the fin field effect transistordevice structure as claimed in claim 5, wherein while forming anamorphous portion of the silicon cap layer over the isolation structure,the silicon cap layer over the fin structure is crystallized.
 7. Themethod for forming the fin field effect transistor device structure asclaimed in claim 5, further comprising: re-crystallizing the amorphousportion of the silicon cap layer to a poly-crystalline portion of thesilicon cap layer.
 8. A method for forming a fin field effect transistordevice structure, comprising: forming a fin structure protruding from asubstrate; forming a liner layer and an isolation structure surroundingthe fin structure; recessing the liner layer and the isolationstructure; growing a cap layer over the fin structure; forming a firstgate dielectric layer covering the cap layer, the liner layer, and theisolation structure, wherein a portion of the cap layer is consumed;forming a gate structure over the first gate dielectric layer across thefin structure; growing source/drain epitaxial structures on oppositesides of the gate structure; and forming a contact structure over thegate structure, wherein the cap layer and the fin structure are made ofthe same material.
 9. The method for forming the fin field effecttransistor device structure as claimed in claim 8, wherein the cap layerhas a first thickness before forming a first gate dielectric layer, thecap layer has a second thickness after forming a first gate dielectriclayer, and the first thickness is greater than the second thickness. 10.The method for forming the fin field effect transistor device structureas claimed in claim 8, wherein the cap layer has a protruding portioncovering the liner layer and the isolation structure.
 11. The method forforming the fin field effect transistor device structure as claimed inclaim 8, wherein the source/drain epitaxial structures are formed overthe cap layer adjacent to the isolation structure.
 12. The method forforming the fin field effect transistor device structure as claimed inclaim 8, further comprising: removing the first gate dielectric layerand recessing the liner layer and the isolation structure; and forming asecond gate dielectric layer covering the fin structure and theisolation structure, wherein the cap layer protrudes from a sidewall ofthe fin structure.
 13. A method for forming a fin field effecttransistor device structure, comprising: forming a fin structure over asubstrate; forming a liner layer and an isolation structure surroundinga bottom portion of the fin structure; cleaning the fin structure;forming a cap layer over the fin structure and the liner layer;depositing a gate dielectric layer over the cap layer and the isolationstructure; forming a work function layer and a gate electrode layer overthe gate dielectric layer across the fin structure; and forming acontact structure over the gate electrode layer, wherein a thickness ofthe cap layer is reduced after depositing the gate dielectric layer, andwherein the cap layer and the fin structure are made of the samematerial.
 14. The method for forming the fin field effect transistordevice structure as claimed in claim 13, wherein a sidewall of the caplayer is aligned with a sidewall of the liner layer after depositing thegate dielectric layer.
 15. The method for forming the fin field effecttransistor device structure as claimed in claim 13, wherein the linerlayer and the isolation structure is recessed after cleaning the finstructure.
 16. The method for forming the fin field effect transistordevice structure as claimed in claim 13, further comprising: trimmingthe fin structure before cleaning the fin structure, wherein the linerlayer and the isolation structure is recessed after trimming the finstructure.
 17. The method for forming the fin field effect transistordevice structure as claimed in claim 16, wherein the fin structurecomprises a protruding portion after cleaning the fin structure, and thecap layer is formed over the protruding portion.
 18. The method forforming the fin field effect transistor device structure as claimed inclaim 16, wherein a middle portion of the fin structure is wider than abottom portion of the fin structure.
 19. The method for forming the finfield effect transistor device structure as claimed in claim 13, furthercomprising: removing the gate dielectric layer, wherein a protrudingportion of the fin structure formed after removing the gate dielectriclayer is separated from the liner layer.
 20. The method for forming thefin field effect transistor device structure as claimed in claim 8,wherein the cap layer and the fin structure are made of silicon.